This invention relates generally to apparatus, a form and a method for making an air formed, reinforced fibrous web and to a reinforced absorbent formed by such a web. The absorbent can be used for applications such as disposable diapers, child's training pants, feminine care articles, incontinence articles, bandages and the like.
Absorbent structures, such as for disposable absorbent garments, may include absorbent cores conventionally formed by air forming or air laying techniques. For example, the manufacture of the absorbent core may begin by fiberizing a fibrous sheet of cellulosic or other suitable absorbent material in a conventional fiberizer, or other shredding or comminuting device, to form discrete fibers. In addition, particles of superabsorbent material are mixed with the discrete fibers. The fibers and superabsorbent particles are then entrained in an air stream and directed to a foraminous forming surface upon which the fibers and superabsorbent particles are deposited to form an absorbent fibrous web. In addition, bonding agents or other strengthening components may be incorporated to provide a more stabilized web.
Other techniques are also employed to form webs of stabilized absorbent material. Such techniques have included dry-forming techniques, wet-laying techniques, foam-forming techniques, and various wet-forming techniques. The resulting webs of absorbent material have included absorbent fibers, natural fibers, synthetic fibers, superabsorbent materials, binders, and strengthening components in desired combinations. However formed, the absorbent web may then be stored or immediately directed for further processing (e.g., being cut into individual absorbent cores) and assembly with other components to produce a final absorbent article.
Absorbent materials have also been strengthened by adding reinforcing members on at least one side of the absorbent structure. Such reinforcement materials have included reinforcement filaments, tissue layers, fabric layers and netting materials. It is also known to add staple binder fibers to the absorbent materials upon formation of the absorbent core. The binder fibers are activated by heat to produce adhesion of the absorbent materials. Integrity of the absorbent core is desirable to avoid bunching, clumping, cracking and separating of the absorbent core in either a wet or a dry state. This improves the fit and comfort to the wearer even after the article receives insults. Sagging and drooping of the absorbent article can cause gaps between the article and the wearer's body which may lead to leaking. As absorbent cores are made both thinner and narrower (particularly in the crotch region), stresses encountered in manufacture and use can be high, requiring reinforcement. In manufacture, tension on the absorbent core can be particularly high during start up and shut down of processing machinery. In use, the lack of integrity can make the absorbent article fit poorly and impact product performance by breaking up the absorbent core, and thereby inhibiting fluid control, liquid handling and wicking which can contribute to leaking.
Co-assigned European Patent Publication No. 0 467 409 A1 discloses one attempt to reinforce an absorbent pad using a scrim material. In that disclosure, a netting or scrim material is used in which some strands have an inner core of one material and an outer sheath of a second material. The scrim is introduced into a forming chamber in which it is incorporated into a fibrous matrix. The second material of the sheath has a lower melting point than the first material of the core. After incorporation of the scrim into the fibrous matrix, the absorbent web formed is heated to melt the sheath for bonding the scrim to the fibers in the matrix. This requires an extra step in the manufacture of a reinforced absorbent.
European Publication No. 0 467 409 also discloses a method for establishing the position of the scrim within the fibrous matrix. Essentially, the location at which the scrim is introduced into the forming chamber is changed to change the depth at which the scrim will be located in the fibrous matrix. The later the scrim is introduced to the forming chamber, the nearer to the top or radially outer surface of the fibrous matrix on the forming drum the scrim will be located. The earlier the scrim is introduced into the forming chamber, the nearer to the bottom or radially inner surface of the fibrous matrix the scrim will be located. However, it is difficult to control placement of the scrim within a fibrous matrix, not only as to its depth within the matrix, but also its lateral position. The high rate flow of air within the forming chamber makes it difficult to maintain control of the scrim. Failure to properly position the scrim within the fibrous matrix can compromise its ability to reinforce an absorbent produced from the fibrous matrix and/or cause the scrim to become entangled in a scarfing roll or other absorbent forming device used to shape the web. If the scrim is laid directly on the forming surface of an air forming machine, it would reinforce the absorbent web only weakly. However, if the web is positioned near the top of the fibrous web, it will become entangled with the scarfing roll of the machine, causing the machine to stop operating until the entanglement is cleared. It will be appreciated that accuracy and consistency in the position of the scrim within the thickness of the absorbent web is desirable.